Automatic three-way valve

ABSTRACT

The present invention relates to a method and apparatus incorporating an automatic, three-way valve having inlet, outlet and drain passages and a close-open timing mechanism. The timing mechanism is adjusted to a predetermined period of time in order to close the drain passage and then open the outlet passage or vice-versa automatically after a predetermined period of time in response to the starting or stopping of an external source of pressurized fluid being directed to the three-way valve.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional application Ser.No. 60/034,087 filed Dec. 30, 1996 entitled AUTOMATIC THREE-WAY VALVE.

FIELD OF THE INVENTION

The present invention relates to valves and particularly to automaticthree-way valves and the method for using same with filters operatingwith filter aid material, such as diatomaceous earth, in order toprevent such filters from transferring fine particles to the filteredfluid area at the beginning of the filtering operation when the cake isnot yet uniformly disposed around the filter element and in many otherapplications.

BACKGROUND OF THE INVENTION

Three-way valves have many industrial uses and are common in all kindsof assemblies. Most three-way valves are ball valves, manually operatedin most cases. In order to operate such valves automatically, anelectric or hydraulic motor, or an actuator, must be mounted on the ballvalve to shift the interconnection and communication between the valvepassages. Actuators and electric motors are both unwieldy, expensive andcomplex. In addition, ball valves also suffer from a fundamentalshortcoming, in that their sealing is achieved by a close fit betweenthe ball surface and the surface of a rigid seat mounted on the valvebody. The relatively large friction area is sensitive to entrapped sandor other particles, causing the valve to seize and interfere with theoperation of changing the state of communication between the valvepassages.

SUMMARY OF THE INVENTION

In accordance with a broad aspect of a preferred embodiments of thepresent invention, there is provided a method and apparatusincorporating an automatic valve, preferably a three-way valveconstructed of a housing having inlet, outlet and drain passages andincluding an internal close-open timing mechanism. The timing mechanismis adjusted to a predetermined period of time in order to close thedrain passage and open the outlet passage or to close the outlet passageand open the drain passage. The opening and closing of passages occursautomatically after a predetermined period of time in response to thestarting or stopping of an external source of pressurized fluid such asa pump which provides pressurized fluid to the three way valve.

The automatic three way valve, in accordance with the present invention,comprises a housing having inlet, outlet and drain passages and anhydraulic unit connected to the housing and to an internal movable shaftmoving with two stops set apart a predetermined distance and betweendrain passage and outlet passage. A sealing flange is located around themovable shaft and disposed between the two stops. The stops are adjustedwith respect to each other so that the sealing flange moves into sealingrelationship with either the outlet or the drain passages. The movableshaft is adjusted to move linearly and freely through a central aperturelocated on the central area of the sealing flange. The movement of theshaft is limited to the distance traveled until one of the two stopspushes against the sealing flange in order to open either one of theoutlet or drain passages and closing the other one of the passages.Controlling the period of time between the entering of pressurized fluidto the inlet passage of the three way valve from a source of pressurizedfluid which flows through the inlet passage to the drain passage untilthe opening of the outlet passage and the closing of the drain passageis an important aspect of the present invention. This period of time iscontrolled by adjusting the distance between the two stops located onthe movable shaft and the size of the passage of pressurized fluidlocated on the hydraulic unit. A control valve, preferably of arelatively small size, is connected to the pressurized fluid passagelocated on the hydraulic unit. The control valve is provided in order tocontrol the size of the opening of the pressurized fluid passage and theperiod of time between the opening or closing of the pressurized fluidflow to the valve and the time of the opening or closing of the outletor the drain passages.

The method and apparatus of the automatic three way valve described andclaimed in the present invention are preferably for the use with filtersusing filter aid material, such as diatomaceous earth (DE), to preventpenetration of fine particles, usually sediments, to the filtered fluidarea which would result in the filtered fluid being contaminated withthe fine particles during the first stages of filtration when the cakeof filter aid material has still not yet or not completely built itselfup around the filter element. The present invention provides featuresallowing the fine particles to drain separately from the filtered fluidfor a predetermined time. After the predetermined period of time haspassed, the drain passage automatically closes and the flow of filteredfluid from the filter is directed through the outlet passage to afiltered fluid collection area, such as a pool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an automatic three wayvalve constructed in accordance with the preferred embodiment of thepresent invention;

FIG. 2 is a sectional view taken along line 2--2 of the automatic threeway valve illustrated in FIG. 1;

FIG. 2A is a schematic view an automatic three way valve constructed inaccordance with the principles of the present invention connected to apump and a filter;

FIG. 3 is a sectional view along the center of the automatic three wayvalve constructed in accordance with the preferred embodiment of thepresent invention;

FIG. 4 is a sectional view of an automatic three way valve constructedand illustrated in accordance with another preferred embodiment of thepresent invention; and

FIG. 5 is a sectional view of another embodiment of an automatic threeway valve similar to the one illustrated in FIG. 4 but with a fewdistinctions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1, FIG. 2 and FIG. 2A which illustrate anautomatic three-way valve 2 constructed and operative as a preferredembodiment of the present invention. Automatic 3-way valve 2 isconnected by a pressure line 3 to a pump 5 and by a line 7 to the outletof a filter 9, as shown in FIG. 2A. Automatic 3-way valve 2 compriseshousing 4 having inlet passage 6, internal passage 8, outlet passage 10and drain passage 12. Fluid entering inlet passage 6 of 3-way valve 2from a line 7 connected to an external source, such as a filter outlet11 of a filter 9, can flow out from the 3-way valve through drainpassage 12. Drain passage 12 is constructed from a drain sleeve 14forming a through passage 16 and a conically shaped flange 18 extendingoutwardly from drain sleeve 14. Drain passage 12 is connected to housing4 by compression ring 20 being threadably secured to the housingshoulder 26 by the threaded interconnection portion 22. The conicallyshaped flange 18 is sealed between the compression ring 20 and thehousing shoulder 26 by O-Ring 24 located between the conic flange 18 andhousing shoulder 26. A sealing flange 28 is typically provided with asealing surface 29, such as a rubber ring 30. The rubber ring 30 ispreferably constructed with a U shaped cross-section adapted to fit overthe outer circumferential surface of sealing flange 28. It is alsowithin the scope of the invention to shape the rubber ring 30 with someother cross sectional configuration or to construct the ring of someother material. Sealing flange 28 is also provided with aperture 32located generally at the center thereof. Sealing flange 28 is adapted tomove linearly between internal passage 8 and drain passage 16 in orderto open one passage while moving to close the other passage and viceversa. Linear movable shaft 34, having first and second ends is locatedwithin the central area of 3-way valve 2 and extends through aperture32. Stops 36 and 38 are fixedly connected to linear movable shaft 34 andare disposed on either side of sealing flange 28. The stops 36 and 38are disposed a predetermined distance between each other and betweenthemselves and the closest respective side of sealing flange 28. Thestops 36 and 38 are adapted to push flange 28 as shaft 34 moves in alinear direction to open either one of the two passages, internalpassage 8 or drain passage 16 and to close the other of the passages.First end 40 of linear movable shaft 34 extends through and is supportedby support bearing 42 connected to sleeve drain 14 by ribs 44. Secondend 46 of movable shaft 34 is connected to a support plate 48 locatedwithin hydraulic unit 50 which is connected to housing 4. A compressionring 52 secures a first cap 54, a diaphragm 56 and second cap 58 ofhydraulic unit 50 by means such as with a threadable interconnectionportion 60 to housing 4. Diaphragm 56, located between first cap 54 andsecond cap 58, divides hydraulic unit 50 into first and secondcompartments 62 and 66. First compartment 62, located between diaphragm56 and first cap 54, is in flow communication with pressure passage 64.The pressure passage 64 is adapted to take in pressurized fluid flowingfrom external source of pressurized fluid such as pump to compartment 62in order to effect the movement of linear movable shaft 34 and to reliefsuch pressure. Second compartment 66 provided with support plate 48 andbias spring 68 is located between diaphragm 56 and second cap 58. Biasspring 68 compress support plate 48 in order to effect the movement ofmovable shaft to one direction. Compartment 66 communicate with reliefpassage 70 through elongated holes 72 located on shoulder 73. Shoulder73 located on one end of housing 4 and second cap 58 are sealed byO-Rings 74 disposed between said second cap and said shoulder. O-Rings74 also seals between holes 72. Linear movable shaft 34 moves back andforth through aperture 76 and O-Ring 78 both disposed generally at thecenter of second cap 58.

Description of operation of the three way valve in accordance with theEmbodiment of FIGS. 1, 2 and 2A

Fluid from external source such as outlet of a filter enters 3-way valve2 through inlet passage 6 and exits the valve through drain 12 passage.Simultaneously pressurized fluid from a source such as a pump entersthrough passage 64 to compartment 62 and presses diaphragm 56, supportplate 48, and movable shaft 34 against bias spring 68 in order to movemovable shaft 34 through aperture 32 and stop 36 toward sealing flange28. Such movement continues until stop 36 pushes sealing flange 28 toopen passage 8 and close passage 16 in order to allow the flow frominlet passage 6 to flow through passage 8 and then to outlet passage 10.Such flow continues until the pressurized fluid to passage 64 isshut-off as a result of the shut-off of its source such as a pump. Thenbias spring 68 pushes support plate 48 and moves movable shaft 34 toexhaust the pressurized fluid from compartment 62 out through passage 64and to draw in air from the atmosphere to compartment 66 through passage70. Movable shaft 34 moves freely through aperture 32 and stop 38 movestoward flange 28 until the stop pushes sealing flange 28 to open passage16 and close passage B. A person with technical skills will understandthat the predetermined distance between sealing flange 28 and one of thestops 36 or 38 acts as a timer indicating the time of occurrence ofeither opening or closing of passages 8 or 16 after the beginning or theshut-off of flow entering 3-way valve 2. The distance between the twostops 36 and 38 and the size of passage 64 establish the time periodpassing from the time of the opening or closing of an external source,such as the opening or shutting-off of the pump from the time of theopening or closing of one of passages 8 or 16.

Reference is now made to FIG. 3 which illustrates another preferredembodiment of an automatic 3-way valve 302, constructed and operative inaccordance with the present invention, and similar to the embodiment ofFIGS. 1, 2, and 2A. The portions of structural elements, of this secondembodiment and the remaining embodiments, which are substantiallyidentical to corresponding structure in the embodiment of FIGS. 1, 2,and 2A, as to the description of their function, their operation andtheir design is the same throughout the present specification. Automatic3-way valve 302 includes a housing 304 having three passages. Fluidflows to 3-way valve 302 from an external source, such as the outlet ofa filter, passes through inlet passage 306, through passage 308 andfinally out from 3-way valve 302 through drain passage 310. Drainpassage 310 is adapted to output fluid mixed with sediments, whennecessary, from valve 302. Outlet sleeve 314 has an outlet passage 312at one end and an inlet passage 316 at the other opposite end. Aconically shaped flange 318, extending outward from outlet sleeve 314,is disposed in abutting relation to housing shoulder 326 of housing 304and is secured thereto by compression ring 320. The compression ring 320is secured, by conventional means such as threaded section 322, in sucha manner that O-Ring 324 seals between the housing shoulder 326 andconically-shaped flange 318.

Sealing flange 328 is typically provided with a sealing surface, such asa rubber ring 330. The rubber ring 330 is preferably constructed with agenerally U shaped cross-section adapted to fit over the outercircumferential surface of sealing flange 328. It is also within thescope of the invention to shape the rubber ring 330 with some othercross sectional configuration or to construct the ring of some othermaterial. Sealing flange 328 is also provided with aperture 332 locatedgenerally at the center thereof. A sealing flange 328 is adapted to movelinearly between passage 308 and passage 316 in order to open onepassage and close the other passage and vice versa. Shaft 334, havingfirst and second ends 340 and 346, is located in the central area of3-way valve 302 and extends through aperture 332 located on flange 328.Stops 336 and 338 are connected to movable shaft 334 and are located ata predetermined distance between each other and between themselves andfrom the closest side of flange 328. Stops 336 and 338 are preferablypositioned to press against flange 328 in order to move and open eitherpassage 308 or 316 while beginning to move and close the other one.First end 340 of movable shaft 334 extends through support bearing 342connected to drain sleeve 314 by ribs 344. Second end 346 of movableshaft 334 is connected to support plate 348 located in a hydraulic unit350 which is secured to housing 304. Compression ring 352 secures firstcap 354 of hydraulic unit 350, diaphragm 356 and second cap 358 ofhydraulic unit 350 to housing 304 by means such as threadable section360. Diaphragm 356, located between first cap 354 and second cap 358,divides hydraulic unit 350 into first and second compartments 362 and366. First compartment 362, located between diaphragm 356 and first cap354, is in flow communication with a relief passage 364 extendingthrough cap 354. Relief passage 364 is adapted to pass fill and exhaustair between the compartment 362 and the atmosphere about the valve 302during the movement of movable shaft 334. First compartment 362comprises also a support base 348 connected to movable shaft 334. Thesupport base 348 supports bias spring 368 and is adapted to pressagainst support plate 348 in order to effect the movement of movableshaft 334 in one direction. Second compartment 366 is located betweendiaphragm 356 and second cap 358. Second compartment 366 communicateswith pressure passage 370 through elongated holes 372 located betweensecond cap 358 and shoulder 373 located on housing 304. A pair ofO-rings 374, located between second cap 358 and shoulder 373, seal thesecond cap 358 to shoulder 373 and also to seal fluid in holes 372.Second cap 358, having an aperture 376 and O-Ring 378 located generallyat the center thereof, is constructed to permit movable shaft 334 tomove back and forth therethrough while still having a seal between theshaft 334 and the second cap 358 to prevent leakage therebetween. It isalso in the scope of the present invention that passage 376 will beconstructed without O-Ring 378.

Description of operation of 3-way valve 304 with reference to FIG. 3.

Fluid flow enters three way valve 304, from a source such as an outletof a filter, through inlet passage 306, then flows through passage 308and finally exits the valve through drain 310. Simultaneously, fluidfrom a source of pressurized fluid, such as pump, enters through passage370, longitudinal holes 372 and into compartment 366. The fluid incompartment 366 presses diaphragm 356, support plate 348, and movableshaft 334 against bias spring 368. Linear movable shaft 334 moves freelythrough aperture 332 until stop 338 pushes flange 328 to open passage316. Further movement of shaft 334 causes flange 328 to close againstpassage 308 with seal 330 so that the fluid from inlet passage 306 wouldflow to outlet passage 312. When pressurized fluid stops flowing as aresult of shut-off of the source of pressurized fluid, such as a pumpshown in FIG. 2A, bias spring 368 presses against support plate 348,diaphragm 356 and movable shaft 334 to move stop 336 towards flange 328.By this movement, air from the atmosphere surrounding valve 302 is drawninto compartment 362 through passage 364 and pressurized fluid isexhausted from compartment 366 through passage 370. Movable shaft 334moves freely through aperture 332 until stop 336 pushes flange 328 toopen passage 308 and close passage 316. The shaft 334 moves in thisdirection, in order to open drain passage 310 so that it can receiveflow coming from inlet passage 306, when the flow starts flowing fromthe external source.

Reference is now made to FIG. 4 which illustrates an automatic three-wayvalve 402 constructed and operative in accordance with another preferredembodiment of the present invention. Three-way valve 402 comprises ahousing 404 assembled from first and second main parts 406 and 410.First main part 406 has a flange 408 provided on its end and second mainpart 410 has a flange 412 provided on its end. First and second mainparts 406 and 410 are connected to each other by conventional means,such as for example screws 414 which extend through flange 408 andflange 412. Conically shaped flange 416, having a passage 418 disposedsubstantially in its center, is secured at its circumference areabetween flange 408 and flange 412. Inlet passage 420 of 3-way valve 402,located in the second main part 410, is adapted to receive fluid flowfrom an external source of pressurized fluid such as the outlet of afilter. Drain passage 422, located in the first main part 406, isadapted to output the flow of fluid, generally mixed with sediments,flowing from inlet 420, and through passage 418 to a location outside ofthe 3-way valve. Outlet passage 424 and inlet passage 426 of outletsleeve 428 are located at the end of second main part 410 of 3-way valve402 and adapted to outlet fluid flow therefrom. Flange 430, locatedbetween passage 418 and passage 426, has a sealing ring 432 (preferablyin U shape but can be shaped in other configurations) secured to itscircumference surface and a throughbore or aperture 434 locatedsubstantially at the center of flange 430. Flange 430 is adapted to moveback and forth between passage 418 and passage 426 in order to open onepassage and close the second one. Movable shaft 436, having first andsecond ends, is located substantially at the center of 3-way valve 402and extends through aperture 434 of flange 430 to transfer linearmovement to the flange 430. Movable shaft 436 is provided with two stops438 and 440 connected thereon and located on both sides of flange 430 ata predetermined distance set so that when shaft 436 moves in onedirection, stop 440 moves flange 430 away from inlet passage 426 andtowards passage 418, and when shaft 436 moves in the other directionstop 438 moves flange 430 to open passage 418 and close inlet passage426. Bearing 442 connected to outlet sleeve 428 by ribs 444 is adaptedto support movable shaft 436 which extends through bearing 442 by itsfirst end. Movable shaft 436 is adjusted to move freely through aperture434 and transfer linear movement to flange 430 in such manner that thelinear movement of shaft 436 only effects the movement of flange 430when one of stops 440 or 438 pushes flange 430 in the direction that itis free to move. Piston 446, with O-Ring 448 provided in itscircumference area, is connected to second end (typically threaded) ofmovable shaft 436 by conventional means such as threaded nuts 450 andreciprocates in a cylinder 452. Cylinder 452, located in first main part406, is open at one end and is enclosed with a cap 454 having a reliefpassage 456. The cap 454 is secured to the end of cylinder 452 byconventional means such as a threaded section 458. Piston 446 isadjusted to move back and forth inside cylinder 452 and to divide thecylinder into two compartments 460 and 462. Compartment 460, located onone side of piston 446, is in communication with relief passage 456. Therelief passage 456 is adjusted to ventilate air in or out fromcompartment 460 during the linear movement of piston 446. Bias spring461, located within compartment 460, is adapted to bias the linearmovement of piston 446 in a first direction. Second compartment 462,located at the other end of piston 446, communicates with pressurepassage 464 through longitudinal hole 466 located on ribs 468. Pressurepassage 464 is adapted to intake and exhaust pressurized fluid or gas toand from compartment 462. The flow of pressurized fluid or air tocompartment 462 is controlled by an external source of pressurized gasor fluid, such as pump, in order to provide linear movement of piston446 in the second direction. On the opposite side of cap 454 is providedaperture 470 located on cylinder 452 adapted to allow for the intake andexhaust of gas or fluid through pressure passage 464 so that movableshaft 436 moves linearly back and forth through aperture 470.

Description of the operation of alternative embodiment of a 3-way valveas illustrated in FIG. 4.

Fluid flow from an external source such as the outlet of a filter entersvalve 402 through inlet passage 420 and flows through passage 418 toexit through drain passage 422. Simultaneously, pressurized fluid from asource of pressurized fluid, such as a pump (See FIG. 2A), enterspassage 464, holes 466 and compartment 462 in order to drive piston 446and movable shaft 436 against bias spring 461. Movable shaft 436 movesfreely through aperture 434 until stop 440 pushes against flange 430 toopen passage 426 and close passage 418 so that the flow of pressurizedfluid from inlet 420 is directed to flow through outlet passage 424.Valve 402 remains in the same position until pressurized fluid tocompartment 462 is shut-off as a result of a shut off of the externalpressure source, i.e. the pump. Then, bias spring 461 presses piston 446and linear movable shaft 436 to effect a movement of linear shaft 436through aperture 434. During the movement of shaft 436 and stop 438toward flange 430, pressure from compartment 462 is exhausted to theoutside atmosphere through passage 464 while air is drawn intocompartment 460 from the atmosphere through passage 456. Movable shaft436 continues to move freely through aperture 434 until stop 438 pushesagainst flange 430 to open passage 418 and close inlet passage 426. Thismovement enables valve 402 to receive the coming flow from an externalsource such as the outlet of a filter through inlet passage 420 and thento direct the flow through passage 418 to drain 422.

Reference is now made to FIG. 5 which illustrates an automatic three-wayvalve 502 constructed and operative in a manner similar to the preferredembodiment of the present invention, as shown and described with respectto the configuration shown in FIG. 4 with some small variations. Threeway valve 502 has a housing 504 assembled from first and second mainparts 506 and 510, respectively. First main part 506 has a flange 508provided on the end thereof and second main part 510 has a flange 512provided on the end thereof. First and second main parts 506 and 510 areconnected by means such as bolts 514 which interconnect flange 508 andflange 512. Conically shaped flange 516, having a passage 518 disposedsubstantially in its center, is secured by a section of itscircumference between flange 508 and flange 512. Inlet passage 520,located in second main part 510, is adapted to receive fluid flow froman external source of pressurized fluid such as an outlet of a filterinto valve 502 so that the fluid flows and exhausts through drain outletpassage 524 located on the second main part 510. Drain outlet passage524 and drain inlet passage 526 of drain sleeve 528 are located in theend of second main part 510 and are adapted to drain fluid generallymixed with sediments from valve 502 when necessary. Sealing flange 530,located between passage 518 and inlet drain passage 526 is provided witha sealing ring 532, preferably with a U shaped cross section (but withinthe scope of the invention, to be shaped in other configurations,secured to the circumferential area of the sealing flange 530. Flange530 has an aperture 534 located substantially in the center thereof.Flange 530 is adapted to move back and forth between passage 518 anddrain passage 526 in order to close one of passages 518 or 526 and openthe other. Movable shaft 536, having first and second ends, is locatedsubstantially at the center of valve 502 and extends with its first endthrough aperture 534 located on sealing flange 530. Stops 538 and 540are connected to the first end portion of movable shaft 536 on bothsides of sealing flange 530 in such manner that when shaft 536 moves inone direction, stop 538 presses against and moves sealing flange 530 toopen passage 518. Further movement of the shaft 536 in the samedirection causes sealing flange 530 to abut against and sealingly closepassage 526. When shaft 536 moves in the other opposite direction, stop540 pushes sealing flange 530 to open drain inlet passage 526 andeventually sealingly close against passage 518. Piston 546, having aseal 548 provided on its circumference, is connected to a second end ofmovable shaft 536 by conventional means such as threaded nuts 550 whichare threadably attached to movable shaft 536 so as to secure piston 546thereto. Cap 554, having a relief passage 556, is connected to the endof cylinder 552 by means such as a threaded section 558. Piston 546 isadjusted to move linearly back and forth inside cylinder 552 so as todivide cylinder 552 into two compartments 560 and 562. Compartment 560,located on one side of piston 546, is in communication with a pressurepassage 556 that is adjusted to receive or exhaust pressurized fluid toand from compartment 560 during the linear movement of piston 546. Thepressure is supplied to compartment 560 from an external source ofpressurized fluid such as pump in order to effect the linear movement ofpiston 546. Second compartment 562 is provided with a bias spring 563abutted against the other, opposite side of piston 546 and is in flowcommunication with relief passage 564 through longitudinal hole 566located on ribs 568. Relief passage 564 is adapted to provide air flowto and from compartment 562 from the surrounding atmosphere. Aperture570 with O-Ring 572 located on cylinder 552 is provided on the oppositeside of cap 554 and adapted to allow movable shaft 536 to move linearlyback and forth through aperture 570 and O-Ring 572. Control valve 574,located on cap 554, is connected to passage 556 in order to reduce orincrease the size of passage 556.

Description of operation in accordance with FIG. 5.

Fluid flowing from an external source, such as the outlet of a filterenters through inlet passage 520 of valve 502 and flows generally mixedwith sediments outside the valve through drain passage 524.Simultaneously, pressurized fluid enters passage 556, flows throughcontrol valve 574 and into compartment 560 to press piston 546 andmovable shaft 536 against bias spring 563. Air from compartment 562 isexhausted to the atmosphere through relief passage 564. Movable shaft536 moves freely through aperture 534 until stop 538 pushes flange 530to open passage 518 and move towards passage 526 and ultimately to closepassage 526 in order to permit flow flowing from the inlet 520 throughpassage 518 to flow to outlet 522. Such position of valve 502 remainsuntil pressurized fluid coming to valve 502 stops as a result ofshut-off of the source of pressurized fluid such as pump. Whenpressurized fluid stops flowing to the valve, bias spring 563 movespiston 546 and the movable shaft 536. This in turn causes stop 540 topush flange 530 in order to first open drain inlet passage 526 and thensubsequently, to close passage 518. Fluid is relieved from compartment560 through relief passage 556 and air is drawn into compartment 562from the atmosphere through relief passage 564.

What is claimed is:
 1. An automatic three way valve comprising:a housinghaving an inlet passage, passage to outlet and a passage to drain; alinearly movable shaft disposed in said housing having two stopsseparated by a predetermined distance; a hydraulic unit connected tosaid housing and to said linearly movable shaft to effect linearmovement of said linearly movable shaft, and; a sealing flange having anaperture substantially at the center thereof accommodating said linearlymovable shaft, said sealing flange being movable on said linearlymovable shaft between said passage to outlet and said passage to drainthrough the force of one of said stops on said sealing flange, saidlinearly movable shaft being biased to urge said sealing flange towardsaid passage to outlet by contact with one of said stops, wherein fluidpressure in said inlet passage tends to maintain said sealing flange inposition to close said passage to outlet from said inlet passage despitelimited movement of said linearly moveable shaft.
 2. The three way valveaccording to claim 1 comprising a sealing flange having a seal with a Ushape cross-section.
 3. The valve according to claim 1, wherein saidhydraulic unit includes a diaphram connected to said linearly movableshaft.
 4. The valve according to claim 1, wherein said inlet passage isprovided with fluid under pressure from a source.
 5. The valve accordingto claim 4, wherein said hydraulic unit is provided with fluid underpressure from said source.
 6. The valve according to claim 4, whereinsaid predetermined distance between said two stops effects a time delaybetween the application of pressurized fluid to the hydraulic unit andthe sealing flange opening the passage to outlet to fluid communicationwith the inlet passage.
 7. The valve according to claim 1, wherein saidlinearly movable shaft is biased so that the sealing flange is biasedtoward closing the passage to outlet.
 8. A three way valve comprising:ahousing having an inlet passage to receive fluid coming to said valveunder pressure from a source, a passage to outlet to outlet fluid fromsaid valve and a passage to drain to drain fluid from said valve; ahydraulic unit including a diaphram and an inlet for fluid underpressure from said source; an axially movable member with two stopsprovided thereon, said axially movable member being connected to saiddiaphram of said hydraulic unit and moveable with said diaphram, and; asealing member movably disposed on said axially movable member betweensaid two stops and between said passage to outlet and said passage todrain, said axially movable member being biased to urge said sealingmember toward said passage to outlet by contact with one of said stops,wherein fluid pressure in said inlet passage tends to maintain saidsealing member in position to close said passage to outlet from saidinlet passage despite limited movement of said axially moveable memberuntil pressure on said diaphram has caused said axially movable memberto move sufficiently that one of said stops forces said sealing memberaway from said passage to outlet.
 9. The valve according to claim 8wherein said hydraulic unit comprises at least one compartment being incommunication with a pressurized fluid passage located in said hydraulicunit in order to receive or relieve pressurized fluid in and from saidcompartment in order to effect the linear movement of said axiallymovable member.